Method of winding a tungsten coil on an iron mandrel



Nov. l5, 1955 E. M. BELLOTT 2,723,926

METHOD OF' WINDING A TUNGSTEN COIL ON AN IRON MANDREL Filed OCT.. 30,1952 and Cl/f v y@ BQ 'A'noRNI United States Patent O METHOD F WINDING ATUNGSTEN COIL ON AN IRON MANDREL Emile Melvin Bellott, Cedar Grove, N.I., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa.,a corporation of Pennsylvania Application October 30, 1952, Serial No.317,741

2 Claims. (Cl. 14S-11.5)

This invention relates to coil winding and, more particularly, to amethod for manufacturing miniature incandescent lament coils on an ironmandrel.

One of the requirements for the automatic mounting of the lamp filamentson the lead-n wires of a stem is that the filament be coiled about astraight axis and have uniform length. In the past, it has beencustomary to wind the filament Wire on a molybdenum mandrel, bake thewound coil in a hydrogen atmosphere at 1500 C. and then dissolve out themandrel in an acid solution, suitably a mixture of sulphuric and nitricacids. The molybdenum mandrel was employed to permit the hightemperature bake of the wound coil thus setting the filament structure,insuring that it would be coiled about a straight axis with uniformlyspaced turns, and also cleaning the coil by reducing (in the hydrogenatmosphere) the oxide formed thereon.

One disadvantage in the use of the molybdenum mandrel is its excessivecost. This is extremely undesirable in the present high speed, massproduction, low unit cost manufacture of incandescent lamps and, moreparticularly, miniature incandescent lamps.

Hence, it has been found advantageous according to my invention toemploy a method of coil winding on an iron mandrel. This methodcomprises essentially: (1) drawing the tungsten wire to the proper sizeor diameter in the conventional manner; (2) electrolytically cleaningthe tungsten wire; (3) winding the clean tungsten wire on an ironmandrel; (4) degreasing, annealing and cutting to length; (5) baking thecoils in a hydrogen atmosphere at 850 C.; (6) dissolving out the ironmandrel in hydrochloric acid and cleaning the coils; and (7) inspectingthe coils.

The hydrogen bake at 850 C., employed in conjunction with cleaning ofthe tungsten wire prior to the winding thereof on the iron mandrel,satisfactorily removes the absorbed gases and surface contaminants fromtungsten wire, insures a straight clean filament which is uniform inlength, after the mandrel has been dissolved, with considerable savingin cost of manufacture.

ln its general aspect, the present invention has as its object theelimination of disadvantages and defects of the prior art coil windingon a molybdenum mandrel.

A specific object of the invention is an improved method of incandescentlamp coil winding on an iron mandrel.

Another object is an improved method of filament coil winding with aniron mandrel comprising; drawing the wire to the proper size,electrolytically cleaning the tungsten wire, automatically winding thewire into a coil on an iron mandrel, degreasing, annealing and cuttingthe coil to the proper length, baking the wound coil in a hydrogenatmosphere at 850 C., dissolving the mandrel and cleaning the coil inhydrochloric acid and trisodium phosphate, and finally inspecting thecoils.

Other objects of the invention will become apparent to those skilled inthe art as the description thereof proceeds, both by direct recitationthereof and by implication from the context.

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Referring to the accompanying drawing:

Fig. 1 is a flow chart of the prior art method of coil winding on amolybdenum mandrel.

Fig. 2 is a iiow chart of the method of my invention for winding thefilament coil on an iron mandrel.

Fig. 3 is a perspective view of a miniature incandescent lamp showing afilament therein wound by the method of my invention.

The old method of filament manufacture, charted in Fig. 1, comprisesessentially the following steps: 1) drawing the tungsten wire insuccessive steps by means of conventional wire drawing dies to therequired size or filament wire diameter, (2) Winding the drawn tungstenwire on a molybdenum mandrel on an automatic coil winding machine, 3)degreasing the wound coil in a conventional hot degreasing bath or tank,annealing the degreased coil in a hydrogen furnace, and cutting the coilto the proper length in a trimming or cutting device, (4) baking theformed coil in a dry hydrogen furnace at about l500 C., (5) immersingthe baked coil in a solution of sulphuric and nitric acid to dissolveout the molybdenum mandrel and cleaning the coil in a caustic solutionto neutralize the acid bath, and 6) inspecting the cleaned coil in avisual projection testing apparatus.

The improved cost-reducing method of my invention, charted in Fig. 2,for winding a filament coil on an iron mandrel may comprise: (l) drawingthe tungsten wire to the proper wire diameter in the conventional way,(2) electrolytically cleaning the tungsten wire, washing in hot water,immersing in a caustic solution, washing again in hot Water,neutralizing the caustic bath with hydrochloric acid, and drying in anair oven, (3) winding the clean tungsten wire into a coil on an ironmandrel on an automatic coil winding machine; (4) degreasing, annealingin wet hydrogen at about 850 C. at the rate of approximately 221/2 ft./min. and cutting to length the wound coil in a conventional manner; (5baking 'the clean coil in a wet hydrogen furnace at about 850 C. forapproximately l0 minutes to set the filament structure curved about astraight axis with uniformly spaced turns to insure uniform length andto remove absorbed gases and surface contaminants therefrom; (6)dissolving out vthe iron mandrel and cleaning the coil by alternatelyimmersing it in trisodium phosphate, hot water, and hydrochloric acid;(7) inspecting the coil in a conventional manner.

In Fig. 3 a conventional miniature lamp, such as a Xmas tree lamp, isdesignated by the reference numeral 10. This lamp 10 comprises avitreous envelope 12, a lamp mount 14 sealed to the open end of theenvelope 12 and having mounted thereon a filament 16 manufactured by themethod of my invention, and suitably a base 18 secured by a conventionalcement about the envelope and mount seal.

While a preferred embodiment of my invention has been disclosed it willbe understood that modifications may be made within the spirit and scopeof the invention.

I claim:

l. The method of fabricating a coil and mandrel assembly comprisingelectrolytically cleaning tungsten wire to remove surface contaminantstherefrom, winding the clean tungsten wire on an iron mandrel;degreasing the wound coil, annealing the coil in wet hydrogen at about850 C. to remove all stresses and strains therein, cutting the woundcoil to length, baking the annealed coil in wet hydrogen at about 850 C.for approximately l() minutes to set the coil structure about a straightaxis with uniformly spaced turns to insure uniform length and to removeabsorbed gases therefrom. Y

2. The method of fabricating a coil and mandrel assembly comprisingelectrolytically cleaning tungsten wire to remove surface contaminantstherefrom, washing said wire in hot water, immersing said wire in acaustic solution, washing said wire again in hot water, neutralizing thecaustic on said wire in hydrochloric acid and drying the wire in an airoven, winding the clean tungsten wire on an iron mandrel; degreasing thewound coil, annealing the coil in Wet hydrogenat about 850a C. to remove5 all stresses and strainstherein, Vcutting the wound coil to length,baking the annealed coil in Wet hydrogen at about 850 C. forapproximately 10 minutes toiset the coil structure about afstraight axiswith uniformly spaced turns to insure'uniforrn length and to removeabsorbed gases 10 therefrom. Y

References Cited in the file of this patent UNITED STATES PATENTS RichMar. 27, 1928 Salpeter Apr. 12, 1938 Laise Mar. 10, 1942 Curtis Oct. 3,1944 Zabel Mar. 13, 1945

1. THE METHOD OF FABRICATING A COIL AND MANDREL ASSEMBLY COMPRISINGELECTROLYTICALLY CLEANING TUNGSTEN WIRE TO REMOVE SURFACE CONTAMINANTSTHEREFROM, WINDING THE CLEAN TUNGSTEN WIRE ON AN IRON MANDREL;DEGREASING THE WOUND COIL, ANNEALING THE COIL IN WET HYDROGEN AT ABOUT850*C. TO REMOVE ALL STRESSES AND STRAINS THEREIN, CUTTING THE WOUNDCOIL TO LENGTH, BAKING THE ANNEALED COIL IN WET HYDROGEN AT ABOUT 850*C.FOR APPROXIMATELY 10 MINUTES TO SET THE COIL STRUCTURE ABOUT A STRAIGHTAXIS WITH UNIFORMLY SPACED TURNS TO INSURE UNIFORM LENGTH AND TO REMOVEABSORBED GASES THEREFROM.